A compact engine is employed as a power source in an electric generator and a portable work tool such as a grass-trimmer, a brush cutter, a blower, a chain-saw, and a power cutter.
Such a conventional engine includes a cooling fan provided on one end of a crank shaft for cooling a cylinder. Rotation of the crank shaft causes the cooling fan to rotate, thereby generating cooling air for cooling the cylinder.
Japanese Patent Application. Publication No. H06-123243 discloses a mechanism in which a wind governor is employed to utilize cooling air for controlling operational states (rotation speed) of an engine. Specifically, a governor plate is disposed on an air flow path of the cooling air within a fan case. The governor plate is connected to a throttle valve shaft of a carburetor and is pivotally movable about this throttle valve shaft.
In this mechanism, when the rotation speed of the engine decreases to reduce the strength of the cooling air, the throttle valve shaft is biased in a direction to increase a throttle opening. On the other hand, when the rotation speed of the engine increases to increase the strength of the cooling air, the governor plate causes the throttle valve shaft to pivotally move toward a direction to reduce the throttle opening. With this structure, the rotation speed of the engine is controlled to be substantially constant.
This mechanism is easily configured by simply connecting a small-sized governor plate (wind governor) to the throttle valve shaft and is therefore effective in various types of portable engine-powered work tools that require compact engines.